U.S. Pat. No. 5,018,928 to Hartlepp discloses an automated, train- and track-type material handling and sortation system in which series of cars are pulled by a tug or locomotive unit on a monorail-type track between sortation stations to receive, transport and discharge goods. The cars or trolleys which carry the goods and associated tilt tray structure travel on a monorail-type track shown in cross-section in FIG. 4. Trolleys include a number of inwardly-facing wheels which ride on upper and lower wheel surfaces of the track.
The track itself is described as having a generally I-shaped cross-section with a central, vertical web 90 and upper and lower transverse arms angled outwardly and upwardly to define the wheel surfaces. The track cross-section and location of the wheel surfaces is designed to locate the car against forces in all directions so that the car remains upright and travels along the track in a stable manner.